Risk map and spatial determinants of pancreas disease in the marine phase of Norwegian Atlantic salmon farming sites

Using a Bayesian modeling approach, with and without spatial component, the final model included site latitude, site density, PD history, and local biomass density. Clearly, the PD infected sites were spatially clustered; however, the cluster was well explained by the covariates of the final model. Based on the final model, we produced a map presenting the predicted probability of the PD occurrence in the southern part of Norway. Subsequently, the predictive capacity of the final model was validated by comparing the predicted probabilities with the observed PD outbreaks in 2011.The framework of the study could be applied for spatial studies of other infectious aquatic animal diseases.Pancreas disease (PD) is a viral disease affecting Atlantic salmon (Salmon salar L.,) and rainbow trout (Oncorhynchus mykiss). A necessary cause of the disease is salmon pancreas disease virus, an alphavirus often referred as salmonid alphavirus (SAV). The onset of a PD outbreak is favored by unspecified influential environmental factors. Diagnostic criteria for PD outbreak were described by Taksdal et al., 2007 [1]. So far, 6 subtypes of SAV have been reported worldwide, whereas, only subtypes 2 and 3 have been detected in Norwegian salmonid farming sites [2, Hilde Sindre per communications]. The disease has been a significant problem in salmonid farming industries in Scotland, Ireland, and Norway [2]. An economic modeling study estimated that the direct cost of PD accounting for biological losses, disease controls and treatments, and insurance payment in a Norwegian salmonid site with an approximate of 500,000 smolts to be at least 14.4 million NOK in 2007 [3].The characteristics of SAV and PD outbreaks have been thoroughly reviewed [4-11]. In Norway, PD outbreaks have been reported only during the marine phase. The disease is regarded as endemic in the area along the western coast of Norway from Rogaland county to a firewall at Hustadvika (Figure 1) in M？re and Romsal with few sporad